In most states, if the election is within a certain degree of closeness (like half a percent), it triggers an automatic recount. And that will catch mismatches

In most states, if the election is within a certain degree of closeness (like half a percent), it triggers an automatic recount. And that will catch mismatches between the machine counts and the contents of their ballot boxes, unless you also carefully rig the manual recount - at scale. And altering the count more than a percent or so is a LOT of alteration.